Paint on mating surfaces?

[onthames]

I current have the front rear subframe off the car, trailing arms, struts etc and am in the process of sandblasting them and repainting. What should not be painted? Anywhere the head of the bolt sits? Cos what if over time the coating fails, lowering the torque on the bolt. I'm not painting any mating surfaces where metal is bolted to metal, as this may mess up the tolerances, apart from things that aren't serious like brackets for cables etc - I assume this is the way to do it? Where metal is on metal how do I protect from rust in these unpainted areas?

Basically I'm paranoid I'm gonna paint all these parts and end up fucking them up by not masking the right bits!!!

[reggid]

i think it is fairly straight forward, follow the factory foremost i think, on front subframe everything except the taper holes for the control arms and maybe the main location dowel is fine to paint.

front struts all external except for holes for tie rod, control arm and the axle snout for bearing asm/dust shield, internal shock thread seems to be what's painted

rear trailing arm all except the bearing surface, hole for speed sensor, park brake cable should be fine. people seem to paint the bore for the two (2) small bushes but might depend on what bush material they will use, i'd probably leave as per factory finish

obviously any internal threads keep clean, though you can chase them

i wouldn't be too worried about paint between interfaces of bolt heads unless the factory had it that way

[tha881]

The Restore It channel is good for info like this. I needed to know where the oil level sensor cable bracket bolts to (the one from the sump) as real oem didnt show enough detail. Checked through his engine rebuild series and could identify that it bolted to the large alternator bracket.

He has painted all those items so I'm sure it will be good for reference.

[rix313]

I wouldn't stress about it too much. It is important to be consious you don't lose tollerances due to thick layes of paint but unless you really lather it on it shouldn't be the end of the world. You can apply copper grease to bare metal faces which will help ward off any rust but it is inevitable with any uncoated surface. If you do 'chase a thread' try not to use a tap as these can often have too much 'cut' to them. A good way to clean threads is to take a standard bolt and cut a line with a hacksaw from the base of the thread vertically up towards the head. This gives an edge to remove any paint and stops unwanted cutting.

[flybynite]

If you do 'chase a thread' try not to use a tap as these can often have too much 'cut' to them. A good way to clean threads is to take a standard bolt and cut a line with a hacksaw from the base of the thread vertically up towards the head. This gives an edge to remove any paint and stops unwanted cutting.

If you do a lot of it get a set of thread chasers, very different design to a tap.